Thanks to excellent research by Alfredo Villanueva (see his website for the original photos) it has been established that the marks below were used on pieces (mainly 'Tango' glassware) known to be from the Kralik glassworks, during the 1920s-30s. They are usually acid-etched, but those on the top row are also known to have occurred printed in dark enamel colours. In the case of the curved marks, the curvature may vary from that shown